Spontaneous far-IR emission accompanying transitions of charge carriers between levels of quantum dots

The spontaneous emission of far-infrared radiation (lambda congruent to 10-20 mu m) from diode structures with vertically coupled InGaAs/AlGaAs quantum dots is observed. This emission is due both to transitions of holes and electrons between size-quantization levels in quantum dots and to transitions from the continuum to a level in a quantum dot. It is observed only when accompanied by lasing at short wavelengths (lambda congruent to 0.94 mu m) and, like the short-wavelength emission, it exhibits a current threshold. The spontaneous emission of long-wavelength radiation is also observed in InGaAs/GaAs quantum-well laser structures. This radiation is approximately an order of magnitude weaker than that from quantum-dot structures, and it has no current threshold. (C) 1998 American Institute of Physics.